Dozens of phase II and III clinical trials for traumatic brain injury (TBI) therapies have failed. One reason cited is that the complex mechanisms and injury cascades associated with different types of TBI are not being addressed by drugs with limited modes of action. Progesterone (PROG) has been shown to be a safe and effective treatment for TBI. A phase I/II clinical trial using PROG to treat moderate to severe brain injury found that mortality from severe injury was reduced almost 60% and there was better functional outcome. This trial was replicated with an additional 159 patients in an independent study from abroad. The PIs'current research is seeking even better results by combining PROG with other neuroprotective agents. A logical first step is to examine the conditions that might limit PROG's beneficial effects in a clinical setting. Vitamin D hormone (VDH) is an FDA-approved molecule whose neuroprotective and neurotrophic actions are increasingly being recognized. The PIs'recent research suggests that, for older subjects, VDH deficiency (VDHdef) reduces the beneficial effects of PROG. It has been reported that well over half of older adults are VDHdef, a condition which could exacerbate the outcome of any TBI, and the elderly population is disproportionately subject to TBI. Further, about 30-35% of the American public has been reported to be VDHdef, so patients of any age, including children, presenting with a TBI could be more at risk and have less favorable outcome if they are also VDH deficient. Thus something as simple as VDH could enhance the benefit of PROG treatment as a neuroprotective agent. Both PROG and VDH are natural hormones, synthesized in both males and females, and have distinct, pleiotropic modes of action in CNS repair. These properties make the preclinical testing of combined PROG and VDH a compelling approach to consider for later evaluation and testing in a clinical TBI trial. First, the PIs will determine the optimal dose for combination treatment to enhance PROG's effects on post- traumatic recovery from neurological deficits and resolution of lesion size in male and female rats. Second, they will see whether PROG's effects are compromised in a co-morbid VDH deficient state in old animals and whether supplementing VDH is necessary to promote optimal benefit. Third, they will establish a correlation, if any, between PROG and VDH levels, functional recovery, and serum levels of surrogate serum biomarkers for TBI. To measure the severity of the injury and predict extent of repair, the time course of changes in neurologic outcome and serum levels of TBI markers will be evaluated. Fourth, the PIs will identify mechanisms that contribute to better neuroprotection by combination of PROG with VDH. The PIs will analyze the gene products most significantly changed in response to combination treatment or either agent alone, and most related to brain injury and repair. PUBLIC HEALTH RELEVANCE: Progesterone (PROG) has been shown to be a safe and effective treatment for moderate and severe traumatic brain Injury. There is evidence that its effectiveness can be increased by combining it with Vitamin D hormone (VDH), especially in the elderly. The fact that both PROG and VDH have high safety profiles, act on many different injury and pathological mechanisms, and are easy to administer and inexpensive, make this combination an obvious approach to develop what may become the first successful treatment for traumatic brain injury.